Process for producing polypeptide

ABSTRACT

The present invention relates to a process for producing a desired polypeptide using rat cells. Specifically, the present invention relates to a process for producing the polypeptide which comprises culturing rat cells such as YB2/3HL.P2.G11.16Ag.20 (hereinafter referred to as YB2/0), preferably rat cells to which a recombinant DNA comprising DNA encoding a desired polypeptide such as an immunologically functional molecule is introduced, in a medium which does not contain serum (hereinafter referred to as a serum-free medium). Among the desired polypeptides obtained by the process of the present invention, an antibody obtained by using a transformant of YB2/0 has a high antibody-dependent cell-mediated cytotoxic activity (hereinafter sometimes referred to as ADCC activity) and is useful as a pharmaceutical agent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. application Ser. No. 10/110,997, filedApr. 19, 2002 now U.S. Pat. No. 7,504,256; which is a 371 ofPCT/JP00/07288, filed Oct. 19, 2000; the entire disclosures of each ofwhich are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a process for producing desired apolypeptide using rat cells. Specifically, the present invention relatesto a process for producing the polypeptide which comprises culturing ratcells such as YB2/3HL.P2.G11.16Ag.20 (hereinafter referred to as YB2/0),preferably rat cells to which a recombinant DNA comprising DNA encodinga desired polypeptide such as an immunologically functional molecule isintroduced, in a medium which does not contain serum (hereinafterreferred to as a serum-free medium). Among the desired polypeptidesobtained by the process of the present invention, an antibody obtainedby using a/transformant of YB2/0 has a high antibody-dependentcell-mediated cytotoxic activity (hereinafter sometimes referred to asADCC activity) and is useful as a pharmaceutical agent.

BACKGROUND ART

Polypeptides having immunological functions such as antibodies have beenfound to be suitable for various pharmaceutical uses. For instance, theyare utilized for the alleviation of rejection reaction to renaltransplantation and in pharmaceuticals as antiviral agents for RSVinfection in infants and as anti-cancer agents for breast cancer. It isexpected that the use of antibody-containing pharmaceutical agents willbe increasingly important.

Production of an antibody using a gene encoding the antibody is carriedout by culturing recombinant cells comprising a vector to which a geneencoding the antibody is introduced and then recovering the antibodyproduced in the culture. Such recombinant antibodies are produced intheir complete form only by animal cells, and therefore, it is preferredto use animal cells for the production of recombinant antibodies.

Production of useful substances using animal cells or recombinant animalcells is widely carried out for research and industrial purposes. In aprocess for producing a substance by culturing animal cells, culturingis usually carried out in a medium which contains serum. However, thepresence of serum is liable to cause differences among batches, whichconsiderably affect the yield of cells and the production of substances.Therefore, use of a medium which does not contain serum is desirable inthe culturing of animal cells for the production of substances.

A process of culturing the rat myeloma cell line YB2/3.0Ag30(hereinafter referred to as Y0) in a protein-free medium is known[Cytotechnology, 17, 193 (1995)]. Also known are processes for producingpolypeptides by culturing animal cells in serum-free media [Biotechnol.Prog., 10, 87 (1994); Cytotechnology, 19, 27 (1996); Japanese PublishedUnexamined Patent Application No. 70757/94] and a process for producingpolypeptides by inoculating into a serum-free medium transformed ratcells grown in a medium containing serum and then culturing the cells inthe serum-free medium (PCT National Publication No. 502377/87).

However, there has been no report on a process for producing desiredpolypeptides stably for a long period of time using rat cells adapted toa serum-free medium.

As a culturing method for animal cells, batch culture is mainlyemployed. In the batch culture, cells are inoculated into a fresh mediumand cultured therein for a certain period of time. It is known that whenanimal cells are cultured by batch culture, the cell growth rate and theproductivity of polypeptide are low because of marked deterioration inculturing conditions during the culturing, e.g., exhaustion of nutrientsand accumulation of waste matters from cells. This leads to a loweringof the polypeptide concentration in the culture, thereby raising therelative concentrations of protein components other than the desiredpolypeptide in the culture, such as proteins derived from cells ormedium. As a result, steps for separating and purifying the polypeptidebecome tedious and production costs are increased, which makes theprocess disadvantageous.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a process forefficiently producing a desired polypeptide using rat cells.

The present invention relates to the following (1) to (24).

-   (1) A process for producing a polypeptide which comprises culturing    in a serum-free medium a rat cell line adapted to a serum-free    medium, and recovering the desired polypeptide from the culture.-   (2) The process according to (1), wherein the rat cell line adapted    to a serum-free medium is a rat cell line which can be subcultured    in a serum-free medium for two months or more.-   (3) The process according to (1) or (2), wherein the rat cell is a    myeloma cell or a hybrid cell derived from a myeloma cell.-   (4) The process according to (1) or (2), wherein the rat cell is    YB2/0.-   (5) The process according to any one of (1) to (4), wherein the cell    is a cell to which a recombinant DNA comprising DNA encoding the    desired polypeptide is introduced.-   (6) The process according to any one of (1) to (5), wherein the    culturing is carried out by batch culture, fed-batch culture or    perfusion culture.-   (7) The process according to any one of (1) to (6), comprising    adding at least one member selected from the group consisting of a    nutrient factor and a physiologically active substance to the medium    during the culturing.-   (8) The process according to (7), wherein the nutrient factor is at    least one member selected from the group consisting of glucose, an    amino acid and a vitamin.-   (9) The process according to (7), wherein the physiologically active    substance is at least one member selected from the group consisting    of insulin, transferrin and albumin.-   (10) The process according to any one of (1) to (9), wherein the    desired polypeptide is an immunologically functional molecule.-   (11) The process according to (10), wherein the immunologically    functional molecule is a protein or a peptide.-   (12) The process according to (11), wherein the protein or peptide    is an antibody, an antibody fragment or a fusion protein comprising    an antibody Fc region.-   (13) The process according to (12), wherein the antibody is an    antibody recognizing a tumor-related antigen, an antibody    recognizing an allergy- or inflammation-related antigen, an antibody    recognizing a circulatory disease-related antigen, an antibody    recognizing an autoimmune disease-related antigen, or an antibody    recognizing a viral or bacterial infection-related antigen.-   (14) The process according to (13), wherein the antibody recognizing    a tumor-related antigen is an anti-GD2 antibody, an anti-GD3    antibody, an anti-GM2 antibody, an anti-HER2 antibody, an anti-CD52    antibody, an anti-MAGE antibody, an anti-basic fibroblast growth    factor antibody, an anti-basic fibroblast growth factor receptor    antibody, an anti-FGF8 antibody, an anti-FGF8 receptor antibody, an    anti-insulin-like growth factor antibody, an anti-PMSA antibody, an    anti-vascular endothelial cell growth factor antibody, or an    anti-vascular endothelial cell growth factor receptor antibody; the    antibody recognizing an allergy- or inflammation-related antigen is    an anti-interleukin 6 antibody, an anti-interleukin 6 receptor    antibody, an anti-interleukin 5 antibody, an anti-interleukin 5    receptor antibody, an anti-interleukin 4 antibody, an    anti-interleukin 4 receptor antibody, an anti-tumor necrosis factor    antibody, an anti-tumor necrosis factor receptor antibody, an    anti-CCR4 antibody, an anti-chemokine antibody, or an anti-chemokine    receptor antibody; the antibody recognizing a circulatory    disease-related antigen is an anti-GpIIb/IIIa antibody, an    anti-platelet-derived growth factor antibody, an    anti-platelet-derived growth factor receptor antibody, or an    anti-blood coagulation factor antibody; the antibody recognizing an    autoimmune disease-related antigen is an anti-auto-DNA antibody; and    the antibody recognizing a viral or bacterial infection-related    antigen is an anti-gp120 antibody, an anti-CD4 antibody, an    anti-CCR4 antibody, or an anti-verotoxin antibody.-   (15) The process according to (13), wherein the antibody is an    anti-GD3 human chimeric antibody, a humanized anti-interleukin 5    receptor a chain antibody, or an anti-GM2 human CDR-grafted    antibody.-   (16) The process according to any one of (1) to (15), wherein the    rat cell is cultured while an insulin concentration in the culture    kept is at 10 mg/l or above, followed by culturing while an insulin    concentration in the culture is kept at 10 mg/l or below.-   (17) A process for adapting a rat cell to a serum-free medium, which    comprises inoculating rat cells into a conditioned medium at a cell    density of 1×10⁵ to 1×10⁶ cells/ml.-   (18) The process according to (17), wherein the rat cell is a    myeloma cell or a hybrid cell derived from a myeloma cell.-   (19) The process according to (17), wherein the rat cell is YB2/0.-   (20) The process according to any one of (17) to (19), wherein the    cell carries an introduced recombinant DNA comprising DNA encoding    the desired polypeptide.-   (21) A process for producing a rat cell line adapted to a serum-free    medium, which comprises adapting rat cells to a serum-free medium by    the process according to any one of (17) to (20), and then cloning    the cells.-   (22) A rat cell line adapted to a serum-free medium, which is    obtained by the process according to (21).-   (23) The rat cell line adapted to a serum-free medium according to    (22), wherein the rat cell line is a rat cell line which can be    subcultured in a serum-free medium for two months or more.-   (24) A rat cell line adapted to a serum-free medium, 61-33 γ (FERM    BP-7325).

The cells of the present invention may be any rat cells and arepreferably those to which a recombinant DNA comprising DNA encoding adesired polypeptide is introduced. Preferred rat cells are myeloma cellsand hybrid cells derived from myeloma cells, e.g., Y3 Ag1.2.3. (ATCC CRL1631), Y0 (ECACC No:85110501) and YB2/0 (ATCC CRL 1662). The cells ofthe present invention also include cells which are obtained bysubjecting the above cells to mutagenesis or cell fusion with B cellsobtained by immunization of a non-human mammal with an antigen and whichhave the same properties as the above cells.

The desired polypeptides of the present invention are preferablyeucaryotic cell polypeptides, more preferably mammal cell polypeptides.The eucaryotic cell polypeptides may be artificially modifiedpolypeptides such as fusion polypeptides or partial fragments thereof,so far as a eucaryotic cell polypeptide is contained as a part thereof.

The polypeptides of the present invention include immunologicallyfunctional molecules such as antibodies, biocatalyst molecules such asenzymes, and structure-forming and retaining molecules such asstructural proteins. Preferred polypeptides are immunologicallyfunctional molecules.

The immunologically functional molecules may be any polypeptides such asproteins and peptides that relate to immune reactions in vivo. Examplesof the immunologically functional molecules include interferon moleculessuch as interleukin-2 (IL-2) [Science, 193, 1007 (1976)] andinterleukin-12 (IL-12) [J. Leuc. Biol., 55, 280 (1994)];colony-stimulating factors such as granulocyte colony stimulating factor(G-CSF) [J. Biol. Chem., 258, 9017 (1983)], macrophage colonystimulating factor (M-CSF) [J. Exp. Med., 173, 269 (1992)] andgranulocyte-macrophage colony stimulating factor (GM-CSF) [J. Biol.Chem., 252, 1998 (1977)]; and growth factors such as erythropoietin(EPO) [J. Biol. Chem., 252, 5558 (1977)] and thrombopoietin (TPO)[Nature, 369, 533 (1994)].

An antibody is a protein which is produced in vivo by an immune reactioncaused by stimulation with an exogenous antigen and which has theactivity to specifically bind to an antigen.

The antibodies include antibodies secreted from hybridomas prepared fromspleen cells of an animal immunized with an antigen, and antibodiesprepared by recombinant DNA techniques, i.e. antibodies produced bycells obtained by introducing an antibody-expressing vector carrying agene encoding the antibody into host cells. Concretely, the antibodiesinclude those produced by hybridomas, humanized antibodies and humanantibodies.

A hybridoma is a cell which is obtained by fusing a B cell obtained froma non-human mammal immunized with an antigen with a rat-derived myelomacell and which produces a monoclonal antibody having the desiredantigenic specificity.

The humanized antibodies include human chimeric antibodies and humancomplementarity determining region (hereinafter referred to asCDR)-grafted antibodies.

A human chimeric antibody is an antibody comprising a heavy-chainvariable region (hereinafter, the heavy chain and the variable regionmay be respectively referred to as H-chain and V region, and thus theantibody heavy-chain variable region may be referred to as HV or VH) anda light-chain variable region (hereinafter, the light chain may bereferred to as L-chain and thus the region may be referred to as LV orVL) of an antibody derived from a non-human animal, a heavy-chainconstant region (hereinafter, the constant region may be referred to asC region and thus this region may be referred to as CH) of a humanantibody and a human light-chain constant region (hereinafter thisregion may be referred to as CL) of a human antibody. As the non-humananimal, any animal can be used so far as hybridomas can be prepared fromthe animal. Suitable animals include mouse, rat, hamster and rabbit.

The human chimeric antibodies can be prepared by recovering cDNAsencoding VH and VL from a hybridoma which produces a monoclonalantibody, inserting the cDNAs into an expression vector comprising genesencoding human antibody CH and human antibody CL for a host cell toconstruct a human chimeric antibody expression vector, and introducingthe vector into the host cell to express the antibody.

As the CH for the human chimeric antibodies, any CH of antibodiesbelonging to human immunoglobulin (hereinafter referred to as hIg) maybe used. Preferred are those of antibodies belonging to the hIgG class,which may be of any subclass, e.g., hIgG1, hIgG2, hIgG3 and hIgG4. Asthe CL for the human chimeric antibodies, any CL of antibodies belongingto hIg, e.g., class K or class A, may be used.

A human CDR-grafted antibody is an antibody prepared by grafting theamino acid sequences of the CDR in the VH and VL of an antibody derivedfrom a non-human animal into appropriate positions in the VH and VL of ahuman antibody.

The human CDR-grafted antibodies can be prepared by constructing cDNAsencoding V regions wherein the CDR sequences of the VH and VL of anantibody derived from a non-human animal are grafted into the CDRsequences of the VH and VL of an optional human antibody, inserting theresulting cDNAs into an expression vector comprising genes encodinghuman antibody CH and human antibody CL for a host cell to construct ahuman CDR-grafted antibody expression vector, and introducing theexpression vector into the host cell to express the human CDR-graftedantibody.

As the CH for the human CDR-grafted antibodies, any CH of antibodiesbelonging to hIg may be used. Preferred are those of antibodiesbelonging to the hIgG class, which may be of any subclass, e.g., hIgG1,hIgG2, hIgG3 and hIgG4. As the CL for the human CDR-grafted antibodies,any CL of antibodies belonging to hIg, e.g., class K or class A, may beused.

The immunologically functional molecules include human chimericantibodies, humanized antibodies and single chain antibodies. Examplesof such antibodies include antibodies against ganglioside GD3(hereinafter referred to as anti-GD3 antibodies) and antibodies againsthuman interleukin-5 receptor α-chain (hereinafter referred to asanti-IL-5 receptor α-chain antibodies). An example of the anti-GD3antibodies is anti-ganglioside GD3 human chimeric antibody (hereinafterreferred to as anti-GD3 chimeric antibody) KM-871 (Japanese PublishedUnexamined Patent Application No. 304989/93), and examples of theanti-IL-5 receptor α-chain antibodies are humanized anti-IL-5 receptorα-chain antibody KM8399 (WO 97/10354) and anti-GM2 human CDR-graftedantibodies KM8966, KM8967, KM8969 and KM8970 (Japanese PublishedUnexamined Patent Application No. 257893/98).

As the DNA encoding the desired polypeptide, any DNA capable ofexpressing the polypeptide can be used. Preferred are DNAs encoding theimmunologically functional molecules.

Examples of the expression vectors used in preparing the recombinantvector comprising the DNA encoding the desired polypeptide includepcDNAI, pcDM8 (manufactured by Funakoshi, Co., Ltd.), pAGE107 [JapanesePublished Unexamined Patent Application No. 22979/91; Cytotechnology, 3,133 (1990)], pAS3-3 (Japanese Published Unexamined Patent ApplicationNo. 227075/90), pCDM8 [Nature, 329, 840 (1987)], pcDNAI/Amp(manufactured by Invitrogen Corporation), pREP4 (manufactured byInvitrogen Corporation), pAGE103 [J. Biochem., 101, 1307 (1987)] andpAGE210.

As the promoter, any promoters capable of functioning in the animalcells used in the present invention can be used. Suitable promotersinclude the promoter of IE (immediate early) gene of cytomegalovirus(CMV), SV40 early promoter, the promoter of a retrovirus,metallothionein promoter, heat shock promoter, SRα promoter, etc. Theenhancer of IE gene of human CMV may be used in combination with thepromoter.

As the host cell, any rat cells may be used. Preferred rat cells aremyeloma cells and hybrid cells derived from myeloma cells, e.g., Y3Ag1.2.3., Y0 and YB2/0. The cells of the present invention also includecells which are obtained by subjecting the above cells to mutagenesis orcell fusion with B cells obtained by immunization of a non-human mammalwith an antigen and which have the same properties as the above cells.

Introduction of the recombinant vector into rat cells can be carried outby any of the methods for introducing DNA into the cells, for example,electroporation [Cytotechnology, 3, 133 (1990)], the calcium phosphatemethod (Japanese Published Unexamined Patent Application No. 227075/90)and lipofection [Proc. Natl. Acad. Sci. USA, 84, 7413 (1987); Virology,52, 456 (1973)].

By culturing the cells to which the recombinant vector is introduced bythe above method in an appropriate medium, the desired polypeptide canbe produced in the cells or in the culture supernatant.

Examples of the cells of the present invention include transformant7-9-51 (FERM BP-6691) producing anti-GD3 human chimeric antibody,transformant KM7399 (FERM BP-5649) producing anti-IL-5 receptor α-chainchimeric antibody, transformant KM9399 (FERM BP-5647) producinganti-IL-5 receptor α-chain human CDR-grafted antibody, and transformantsKM8966 (FERM BP-510S), KM8967 (FERM BP-5106), KM8969 (FERM BP-5527) andKM8970 (FERM BP-5528) producing anti-GM2 human CDR-grafted antibodies.

Adaptation of cells to a serum-free medium in accordance with thepresent invention can be carried out, for example, by adapting rat cellssubcultured in a serum-containing medium directly to a commerciallyavailable serum-free medium, or by continuous adaptation (Cell & TissueCulture Laboratory Procedures, JOHN WILEY & SONS 2C:1).

During the process of adaptation to a serum-free medium, the viabilityof cells lowers temporarily, which sometimes causes extinction of cells.Therefore, it is preferred to inoculate cells into a medium for theadaptation to a serum-free medium at a cell density of 1×10⁵ to 10×10⁵cells/ml, preferably 4×10⁵ to 6×10⁵ cells/ml, in order to restore theviability of cells or to keep it high. In one embodiment according tothe direct adaptation method, cells are inoculated into a medium andcultured by an ordinary culturing method for animal cells, e.g., batchculture in a 5% CO₂ incubator at 37° C. until the cell density reaches10×10⁵ to 40×10⁵ cells/ml and then the cells are inoculated into aserum-free medium, followed by repetition of culturing under similarconditions.

The rat cells are inoculated into a serum-free medium at a density of1×10⁵ to 10×10⁵ cells/ml, preferably 4×10⁵ to 6×10⁵ cells/ml, andcultured by an ordinary culturing method for animal cells. After 4 to 7days of culturing, the rat cells whose density reached 10×10⁵ to 40×10⁵cells/ml are selected as the cells adapted to a serum-free medium.

The cells adapted to a serum-free medium are inoculated into a mediumemployed in the batch culture described below at a density of 10×10⁵ to30×10⁵ cells/ml and cultured for 3 to 5 days under the culturingconditions employed in the batch culture described below, wherebysubculturing can be carried out. During the subculturing, it ispreferred to maintain the viability of the cells adapted to a serum-freemedium at 90% or more. In order to maintain the productivity of thedesired polypeptide by the rat cells, e.g. YB2/0 and transformants ofYB2/0, adapted to a serum-free medium, it is desirable to add albumin toa serum-free medium in an amount of 0.1 to 10 g/l, preferably 0.5 to 3g/l.

After the cells of the present invention are adapted to a serum-freemedium, a cloned cell line can be prepared by using the limitingdilution method with a 96-well plate, the colony forming method, or thelike.

Described below is a process for preparing a cloned cell line by thelimiting dilution method.

A cell suspension is diluted and inoculated into wells in such an amountthat the number of cells per well is not more than one, and culturing iscarried out in a 5% CO₂ incubator at 30 to 40° C. using a commerciallyavailable serum-free medium or the like for several weeks. After thecompletion of culturing, the concentration of the desired polypeptide inthe culture supernatant of the cells observed to have grown isdetermined, and the cells having a high productivity of the polypeptideare selected.

Cloning by the colony forming method can be carried out in the followingmanner.

In the case of adherent cells, a cell suspension is diluted and thecells are inoculated into a Petri dish and cultured. After the colonyformation is confirmed, the colony is separated using a ring of apenicillin cap or the like, and the cells are released with an enzymesuch as trypsin and then transferred into an appropriate incubator. Theamount of the desired polypeptide produced is determined, and the cellshaving a high productivity of the polypeptide are selected.

In the case of suspending cells, a cell suspension is diluted and thecells are inoculated into soft agar and cultured. The formed colony ispicked up under a microscope and then subjected to static culture. Theamount of the desired polypeptide produced is determined, and the cellshaving a high productivity of the polypeptide are selected.

By repeating the above procedure, a cloned rat cell line adapted to aserum-free medium and having the desired cell characteristics can beselected.

According to the above process, a rat cell line adapted to a serum-freemedium, preferably a rat cell line which can be subcultured in aserum-free medium for two months or more, can be obtained. A rat cellline which can be subcultured in a serum-free medium for two months ormore is desirable for culturing cells adapted to a serum-free medium fora long period of time.

The rat cell line adapted to a serum-free medium can be subcultured bythe above method for subculturing the cells adapted to a serum-freemedium. An example of such rat cell line adapted to a serum-free mediumis 61-33γ (FERM BP-7325).

Culturing of the cells of the present invention can be carried out byany of general culturing methods for animal cells capable of efficientlyproducing the desired polypeptides, for example, batch culture, repeatedbatch culture, fed-batch culture and perfusion culture. Preferably,fed-batch culture or perfusion culture is employed in order to raise theproductivity of the desired polypeptides.

1. Batch Culture

The serum-free medium used in the process of the present invention is amedium prepared by adding, instead of serum, various physiologicallyactive substances and nutrient factors, as well as carbon sources,nitrogen sources, etc. which can be assimilated by animal cells, to anordinary basal medium employed for the culturing of animal cells.

Examples of suitable media include RPMI1640 medium [The Journal of theAmerican Medical Association, 199, 519 (1967)], Eagle's MEM [Science,122, 501 (1952)], Dulbecco's modified MEM [Virology, 8, 396 (1959)], 199medium [Proceeding of the Society for the Biological Medicine, 73, 1(1950)], F12 medium [Proc. Natl. Acad. Sci. USA, 53, 288 (1965)] andIMDM [J. Experimental Medicine, 147, 923 (1978)]. Preferred are DMEM,F12 medium and IMDM.

To the serum-free medium are added nutrient factors, physiologicallyactive substances, etc. required for the growth of animal cellsaccording to need prior to the culturing.

The nutrient factors include glucose, amino acids and vitamins.

Examples of the amino acids are L-alanine, L-arginine, L-asparagine,L-aspartic acid, L-cystine, L-glutamic acid, L-glutamine, glycine,L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine,L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan,L-tyrosine and L-valine, which may be used alone or in combination.

Examples of the vitamins are d-biotin, D-pantothenic acid, choline,folic acid, myo-inositol, niacinamide, pyridoxal, riboflavin, thiamine,cyanocobalamin and DL-α-tocopherol, which may be used alone or incombination.

The physiologically active substances include insulin, transferrin andalbumin.

As for the concentrations of the nutrient factors, glucose is added togive a concentration of 200 to 6000 mg/l, preferably 3000 to 5000 mg/l.

The amino acids are added, for example, to give the followingconcentrations: L-alanine, 1 to 160 mg/l (preferably 3 to 120 mg/l);L-arginine monohydrochloride, 10 to 1000 mg/l (preferably 30 to 800mg/l); L-asparagine monohydrate, 10 to 200 mg/l (preferably 20 to 150mg/l); L-aspartic acid, 5 to 100 mg/l (preferably 10 to 75 mg/l);L-cystine dihydrochloride, 10 to 200 mg/l (preferably 20 to 150 mg/l);L-glutamic acid, 5 to 200 mg/l (preferably 10 to 150 mg/l); L-glutamine,50 to 2000 mg/l (preferably 100 to 1500 mg/l); glycine, 2 to 100 mg/l(preferably 5 to 75 mg/l); L-histidine monohydrochloride dihydrate, 5 to200 mg/l (preferably 10 to 150 mg/l); L-isoleucine, 2 to 300 mg/l(preferably 4 to 200 mg/l); L-leucine, 5 to 300 mg/l (preferably 10 to200 mg/l); L-lysine monohydrochloride, 10 to 300 mg/l (preferably 20 to250 mg/l); L-methionine, 5 to 100 mg/l (preferably 10 to 75 mg/l);L-phenylalanine, 5 to 200 mg/l (preferably 10 to 150 mg/l); L-proline, 5to 200 mg/l (preferably 10 to 150 mg/l); L-serine, 5 to 200 mg/l(preferably 10 to 150 mg/l); L-threonine, 5 to 200 mg/l (preferably 10to 150 mg/l); L-tryptophan, 1 to 40 mg/l (preferably 2 to 30 mg/l);L-tyrosine disodium dihydrate, 2 to 300 mg/l (preferably 4 to 200 mg/l);and L-valine, 5 to 300 mg/l (preferably 10 to 200 mg/l).

The vitamins are added, for example, to give the followingconcentrations: d-biotin, 0.001 to 0.4 mg/l (preferably 0.002 to 0.3mg/l); calcium D-pantothenate, 0.001 to 10.0 mg/l (preferably 0.002 to7.5 mg/l); choline chloride, 0.1 to 20.0 mg/l (preferably 0.2 to 15.0mg/l); folic acid, 0.005 to 20.0 mg/l (preferably 0.01 to 15.0 mg/l);myo-inositol, 0.01 to 300 mg/l (preferably 0.05 to 200 mg/l);niacinamide, 0.01 to 20.0 mg/l (preferably 0.02 to 15.0 mg/l); pyridoxalmonohydrochloride, 0.01 to 15.0 mg/l (preferably 0.02 to 10.0 mg/l);riboflavin, 0.005 to 2.0 mg/l (preferably 0.01 to 1.5 mg/l); thiaminemonohydrochloride, 0.005 to 20.0 mg/l (preferably 0.01 to 15.0 mg/l);and cyanocobalamin, 0.001 to 5.0 mg/l (preferably 0.002 to 3.0 mg/l).

The physiologically active substances are added, for example, to givethe following concentrations: insulin, 10 to 500 mg/l, preferably 50 to300 mg/l; transferrin, 10 to 500 mg/l, preferably 50 to 300 mg/l; andalbumin, 200 to 6000 mg/l, preferably 700 to 4000 mg/l.

The batch culture is usually carried out at pH 6 to 8 at 30 to 40° C.for 3 to 12 days. If necessary, antibiotics such as streptomycin andpenicillin may be added to the medium during the culturing. Further,control of dissolved oxygen concentration, pH control, temperaturecontrol, stirring and the like can be carried out according to generalmethods employed in the culturing of animal cells.

2. Fed-batch Culture

The serum-free medium used in the process of the present invention is amedium prepared by adding, instead of serum, various physiologicallyactive substances and nutrient factors, as well as carbon sources,nitrogen sources, etc. which can be assimilated by animal cells, to anordinary basal medium employed for the culturing of animal cells.

Examples of suitable media include RPMI1640 medium [The Journal of theAmerican Medical Association, 199, 519 (1967)], Eagle's MEM [Science,122, 501 (1952)], Dulbecco's modified MEM [Virology, 8, 396 (1959)], 199medium [Proceeding of the Society for the Biological Medicine, 73, 1(1950)], F12 medium [Proc. Natl. Acad. Sci. USA, 53, 288 (1965)] andIMDM [J. Experimental Medicine, 147, 923 (1978)]. Preferred are DMEM,F12 medium and IMDM. In addition to the above media, the serum-freemedia described in the above description of batch culture are alsouseful.

To the serum-free medium are added physiologically active substances,nutrient factors, etc. required for the growth of animal cells accordingto need. These additives may be contained in the medium prior to theculturing or may be appropriately added to the culture during theculturing according to need.

The nutrient factors include glucose, amino acids and vitamins.

Examples of the amino acids are L-alanine, L-arginine, L-asparagine,L-aspartic acid, L-cystine, L-glutamic acid, L-glutamine, glycine,L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine,L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan,L-tyrosine and L-valine, which may be used alone or in combination.

Examples of the vitamins are d-biotin, D-pantothenic acid, choline,folic acid, myo-inositol, niacinamide, pyridoxal, riboflavin, thiamine,cyanocobalamin and DL-α-tocopherol, which may be used alone or incombination.

The physiologically active substances include insulin, transferrin andalbumin.

As for the final concentrations of the nutrient factors in the medium orculture, glucose is added to give a final concentration of 200 to 6000mg/l, preferably 1000 to 5000 mg/l.

The amino acids are added, for example, to give the following finalconcentrations: L-alanine, 1 to 960 mg/l (preferably 1 to 640 mg/l);L-arginine monohydrochloride, 10 to 6000 mg/l (preferably 11 to 4000mg/l); L-asparagine monohydrate, 10 to 1200 mg/l (preferably 11 to 800mg/l); L-aspartic acid, 5 to 600 mg/l (preferably 5 to 400 mg/l);L-cystine dihydrochloride, 10 to 1200 mg/l (preferably 11 to 800 mg/l);L-glutamic acid, 5 to 1200 mg/l (preferably 5 to 800 mg/l); L-glutamine,53 to 12000 (preferably 55 to 8000 mg/l); glycine, 2 to 600 mg/l(preferably 2 to 400 mg/l); L-histidine monohydrochloride dihydrate, 5to 1200 mg/l (preferably 5 to 800 mg/l); L-isoleucine, 4 to 1800 mg/l(preferably 4 to 1200 mg/l); L-leucine, 13 to 1800 mg/l (preferably 14to 1200 mg/l); L-lysine monohydrochloride, 10 to 1800 mg/l (preferably11 to 1200 mg/l); L-methionine, 4 to 600 mg/l (preferably 5 to 400mg/l); L-phenylalanine, 5 to 1200 mg/l (preferably 5 to 800 mg/l);L-proline, 5 to 1200 mg/l (preferably 5 to 800 mg/l); L-serine, 5 to1200 mg/l (preferably 5 to 800 mg/l); L-threonine, 5 to 1200 mg/l(preferably 5 to 800 mg/l); L-tryptophan, 1 to 240 mg/l (preferably 1 to160 mg/l); L-tyrosine disodium dihydrate, 8 to 1800 mg/l (preferably 8to 1200 mg/l); and L-valine, 12 to 1800 mg/l (preferably 12 to 1200mg/l).

The vitamins are added, for example, to give the following finalconcentrations: d-biotin, 0.001 to 2.4 mg/l (preferably 0.001 to 1.6mg/l); calcium D-pantothenate, 0.011 to 60 mg/l (preferably 0.011 to 40mg/l); choline chloride, 0.11 to 90 mg/l (preferably 0.11 to 60 mg/l);folic acid, 0.01 to 120 mg/l (preferably 0.01 to 80 mg/l); myo-inositol,0.05 to 1800 mg/l (preferably 0.05 to 1200 mg/l); niacinamide, 0.02 to120 mg/l (preferably 0.03 to 80 mg/l); pyridoxal monohydrochloride, 0.02to 90 mg/l (preferably 0.03 to 60 mg/l); riboflavin, 0.01 to 12 mg/l(preferably 0.01 to 9.8 mg/l); thiamine monohydrochloride, 0.01 to 120mg/l (preferably 0.01 to 80 mg/l); and cyanocobalamin, 0.001 to 30 mg/l(preferably 0.001 to 20 mg/l).

The physiologically active substances are added to the medium orculture, for example, to give the following final concentrations:insulin, 10 to 3000 mg/l, preferably 11 to 2000 mg/l; transferrin, 10 to3000 mg/l, preferably 11 to 2000 mg/l; and albumin, 200 to 36000 mg/l,preferably 220 to 24000 mg/l.

In the present invention, the “final concentration” of a substance isexpressed as the value obtained by dividing, after the final addition ofconcentrated culture medium during the fed-batch culture, the totalweight of the substance contained in the medium and that added to theculture by the total volume of the medium and the concentrated culturemedium added.

In the fed-batch culture, it is preferred to add the physiologicallyactive substances, nutrient factors, etc. at higher concentrations thanusually employed. For example, they are added in an amount of 1/30 to1/3, preferably 1/20 to 1/5 the volume of culture at a time. In the caseof addition to the culture, they are preferably added continuously or inseveral to over ten portions during the culturing. According to theabove-described fed-batch culture which comprises adding thephysiologically active substances, nutrient factors, etc. continuouslyor intermittently in small portions, a high metabolic efficiency ofcells can be attained and the lowering of the finally attained densityof cultured cells due to the accumulation of waste matters in theculture can be prevented. Further, the concentration of the desiredpolypeptide in the recovered culture is higher than that in the batchculture, which facilitates the separation and purification of thepolypeptide and thus improves the productivity of the polypeptide permedium compared with the batch culture.

The fed-batch culture is usually carried out at pH 6 to 8 at 30 to 40°C. for 3 to 12 days. If necessary, antibiotics such as streptomycin andpenicillin may be added to the medium during the culturing. Further,control of dissolved oxygen concentration, pH control, temperaturecontrol, stirring and the like can be carried out according to generalmethods employed in the culturing of animal cells.

3. Perfusion Culture

The serum-free medium used in the process of the present invention is amedium prepared by adding, instead of serum, various physiologicallyactive substances and nutrient factors, as well as carbon sources,nitrogen sources, etc. which can be assimilated by animal cells, to anordinary basal medium employed for the culturing of animal cells.

Examples of suitable media include RPMI1640 medium [The Journal of theAmerican Medical Association, 199, 519 (1967)], Eagle's MEM [Science,122, 501 (1952)], Dulbecco's modified MEM [Virology, 8, 396 (1959)], 199medium [Proceeding of the Society for the Biological Medicine, 73, 1(1950)], F12 medium [Proc. Natl. Acad. Sci. USA, 53, 288 (1965)] andIMDM [J. Experimental Medicine, 147, 923 (1978)]. Preferred are DMEM,F12 medium and IMDM. In addition to the above media, the serum-freemedia described in the above description of batch culture are alsouseful.

To the serum-free medium are added physiologically active substances,nutrient factors, etc. required for the growth of animal cells accordingto need. These additives are preferably added to the medium prior to theculturing or to the medium to be supplied to the culture.

The nutrient factors include glucose, amino acids and vitamins.

Examples of the amino acids are L-alanine, L-arginine, L-asparagine,L-aspartic acid, L-cystine, L-glutamic acid, L-glutamine, glycine,L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine,L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan,L-tyrosine and L-valine, which may be used alone or in combination.

Examples of the vitamins are d-biotin, D-pantothenic acid, choline,folic acid, myo-inositol, niacinamide, pyridoxal, riboflavin, thiamine,cyanocobalamin and DL-α-tocopherol, which may be used alone or incombination.

The physiologically active substances include insulin, transferrin andalbumin.

As for the concentrations of the nutrient factors, the concentration ofglucose is controlled at 500 to 6000 mg/l, preferably 1000 to 2000 mg/l.

The nutrient factors include amino acids and vitamins. The otherphysiologically active substances or nutrient factors are added, forexample, to give the following concentrations: insulin, 4 to 560 mg/l,preferably 20 to 360 mg/l; transferrin, 4 to 560 mg/l, preferably 20 to360 mg/l; and albumin, 80 to 6500 mg/l, preferably 280 to 4500 mg/l.

Examples of the amino acids are L-alanine, L-arginine, L-asparagine,L-aspartic acid, L-cystine, L-glutamic acid, L-glutamine, glycine,L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine,L-phenylalanine, L-proline, L-serine, L-threonine, L-tryptophan,L-tyrosine and L-valine, which may be used alone or in combination. Theamino acids are added, for example, to give the followingconcentrations: L-alanine, 1 to 200 mg/l (preferably 2 to 160 mg/l);L-arginine monohydrochloride, 10 to 1140 mg/l (preferably 30 to 940mg/l); L-asparagine monohydrate, 10 to 250 mg/l (preferably 20 to 200mg/l); L-aspartic acid, 5 to 148 mg/l (preferably 10 to 120 mg/l);L-cystine dihydrochloride, 10 to 350 mg/l (preferably 20 to 300 mg/l);L-glutamic acid, 5 to 320 mg/l (preferably 10 to 270 mg/l); L-glutamine,50 to 3300 (preferably 100 to 1800 mg/l); glycine, 2 to 148 mg/l(preferably 5 to mg/l); L-histidine monohydrochloride dihydrate, 5 tomg/l (preferably 10 to 220 mg/l); L-isoleucine, 4 to mg/l (preferably 4to 370 mg/l); L-leucine, 10 to mg/l (preferably 13 to 370 mg/l);L-lysine monohydrochloride, 10 to 530 mg/l (preferably 20 to mg/l);L-methionine, 4 to 150 mg/l (preferably 4 to 120 mg/l); L-phenylalanine,4 to 310 mg/l (preferably 4 to 260 mg/l); L-proline, 5 to 270 mg/l(preferably 10 to 210 mg/l); L-serine, 5 to 270 mg/l (preferably 10 to220 mg/l); L-threonine, 5 to 350 mg/l (preferably 10 to 300 mg/l);L-tryptophan, 1 to 65 mg/l (preferably 2 to 55 mg/l); L-tyrosinedisodium dihydrate, 4 to 470 mg/l (preferably 8 to 370 mg/l); andL-valine, 10 to 450 mg/l (preferably 11 to 350 mg/l).

Examples of the vitamins are d-biotin, D-pantothenic acid, choline,folic acid, myo-inositol, niacinamide, pyridoxal, riboflavin, thiamine,cyanocobalamin and DL-α-tocopherol, which may be used alone or incombination. The vitamins are added, for example, to give the followingfinal concentrations: d-biotin, 0.001 to 0.44 mg/l (preferably 0.02 to0.34 mg/l); calcium D-pantothenate, 0.01 to 16 mg/l (preferably 0.02 to14 mg/l); choline chloride, 0.1 to 21 mg/l (preferably 0.2 to 16 mg/l);folic acid, 0.01 to 26 mg/l (preferably 0.01 to 21 mg/l); myo-inositol,0.05 to 310 mg/l (preferably 0.05 to 211 mg/l); niacinamide, 0.02 to 26mg/l (preferably 0.02 to 21 mg/l); pyridoxal monohydrochloride, 0.02 to21 mg/l (preferably 0.02 to 16 mg/l); riboflavin, 0.01 to 2.6 mg/l(preferably 0.01 to 2.1 mg/l); thiamine monohydrochloride, 0.01 to 26mg/l (preferably 0.01 to 21 mg/l); and cyanocobalamin, 0.001 to 5 mg/l(preferably 0.002 to 3 mg/l).

In accordance with the present invention, the culture is efficientlyseparated by use of an apparatus usually employed for separating cellsfrom a culture. The concentrated culture containing the cells isreturned to the incubator and a fresh medium is added for supplement thereduced culture, whereby desirable culturing conditions can bemaintained during the culturing process.

The productivity of the desired polypeptide by the cells of the presentinvention can be enhanced by stabilizing the culturing system bydiscarding the proliferated cells from the system according to the cellgrowth rate, apart from the rate of replacement with a fresh medium. Forinstance, it is possible to carry out culturing with a high productivityby discarding the cells from the system at a rate in accordance with thecell growth rate, i.e., discarding 2/5 to 3/5 of all the cells existingin the incubator during the doubling time so that the desired celldensity can be maintained.

The culturing according to the present invention is usually carried outat pH 6 to 8 at 30 to 40° C. for 10 to 40 days. If necessary,antibiotics such as streptomycin and penicillin may be added to themedium during the culturing. Further, control of dissolved oxygenconcentration, pH control, temperature control, stirring and the likecan be carried out according to general methods employed in theculturing of animal cells.

As described above, the desired polypeptide can be produced by culturingthe rat cells of the present invention, allowing the polypeptide to formand accumulate, and recovering the polypeptide from the culture.

In the present invention, it is preferred to carry out the culturingwith the insulin concentration in the culture kept at 10 mg/l or above,preferably 20 mg/l or above in order to grow the cells. On the otherhand, in order to produce the desired polypeptide, it is preferred tocarry out the culturing with the insulin concentration in the culturekept at 10 mg/l or below, preferably 5 mg/l or below. When the mediumfor the former culturing contains insulin, it is not necessary to addinsulin in order to enhance the productivity of antibody. However, theinsulin concentration in the culture is usually kept at 0.01 to 10 mg/l,preferably 0.01 to 5 mg/l.

The methods of adjusting the insulin concentration in the culture areadvantageously employed in the culturing capable of insulinconcentration adjustment, e.g., fed-batch culture and perfusion culture.

In the present invention, the desired polypeptide may be produced by thedirect expression method in which the polypeptide is produced in thehost cells or by the method in which the polypeptide is secreted outsidethe host cells (Molecular Cloning, 2nd ed.).

It is possible to have the desired polypeptide actively secreted outsidethe host cells by applying the method of Paulson, et al. [J. Biol.Chem., 264, 17619 (1989)], the method of Lowe, et al. [Proc. Natl. Acad.Sci. USA, 86, 8227 (1989); Genes Develop., 4, 1288 (1990)], or themethods described in Japanese Published Unexamined Patent ApplicationNo. 336963/93, WO94/23021, etc. That is, the desired polypeptide can beactively secreted outside the host cells by expressing it in the form ofa polypeptide in which a signal peptide is added upstream of thepolypeptide of the present invention by the use of recombinant DNAtechniques.

It is also possible to increase the production of the desiredpolypeptide by utilizing a gene amplification system using adihydrofolate reductase gene or the like according to the methoddescribed in Japanese Published Unexamined Patent Application No.227075/90.

The desired polypeptide produced by the process of the present inventioncan be isolated and purified by general methods for isolating andpurifying polypeptides.

When the polypeptide produced by the process of the present invention isintracellularly expressed in a soluble form, the cells are recovered bycentrifugation after the completion of culturing and suspended in anaqueous buffer, followed by disruption using sonicator, French press,Manton-Gaulin homogenizer, Dynomill or the like to obtain a cell-freeextract. From the supernatant obtained by centrifuging the cell-freeextract, a purified polypeptide preparation can be obtained by usinggeneral methods for isolating and purifying enzymes, i.e., extractionwith a solvent, salting-out with ammonium sulfate, etc., desalting,precipitation with an organic solvent, anion exchange chromatographyusing resins such as diethylaminoethyl (DEAE)-Sepharose and DIAIONHPA-75 (Mitsubishi Kasei Corporation), cation exchange chromatographyusing resins such as S-Sepharose FF (Pharmacia), hydrophobicchromatography using resins such as butyl Sepharose and phenylSepharose, gel filtration using a molecular sieve, affinitychromatography using protein A, chromatofocusing, electrophoresis suchas isoelectric focusing, etc., singly or in combination.

When the polypeptide produced by the process of the present invention issecreted extracellularly, the polypeptide can be recovered in theculture supernatant. That is, the culture is treated by the same meansas above, e.g., centrifugation, to obtain the culture supernatant. Fromthe culture supernatant, a purified polypeptide preparation can beobtained by using the same isolation and purification methods as above.

Among the polypeptides produced by the process of the present invention,immunologically functional molecules, especially antibodies, have a highantibody-dependent cell-mediated cytotoxic activity (ADCC activity) andare useful for the treatment of diseases such as tumor, inflammation andallergy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the change in viable cell density and viability during theculturing of anti-GD3 chimeric antibody-producing cell line 61-33γ (FERMBP-7325) adapted to a serum-free medium.

FIG. 2 shows the change in antibody concentration of anti-GD3 chimericantibody KM-871 during the culturing of anti-GD3 chimericantibody-producing cell line 61-33γ (FERM BP-7325) adapted to aserum-free medium.

FIG. 3 shows the change in viable cell density and viability during theperfusion culture of anti-GD3 chimeric antibody-producing cell line61-33γ (FERM BP-7325) adapted to a serum-free medium.

BEST MODES FOR CARRYING OUT THE INVENTION

Examples of the present invention are shown below.

Example 1 Production of Anti-GD3 Chimeric Antibody

1. Construction of Tandem Expression Vector pChiLHGM4 for Anti-GD3 HumanChimeric Antibody

The expression vector pChi641LGM4 for L-chain of anti-GD3 chimericantibody [J. Immunol. Methods, 167, 271 (1994)] was cleaved withrestriction enzymes MluI (Takara Shuzo Co., Ltd.) and SalI (Takara ShuzoCo., Ltd.) to obtain a fragment of ca. 4.03 kb comprising the L-chaincDNA. Separately, the expression vector pAGE107 for animal cells[Cytotechnology, 3, 133 (1990)] was cleaved with restriction enzymesMluI (Takara Shuzo Co., Ltd.) and SalI (Takara Shuzo Co., Ltd.) toobtain a fragment of ca. 3.40 kb comprising the G418 resistance gene andthe splicing signal. The obtained fragments were ligated using DNALigation Kit (Takara Shuzo Co., Ltd.) and Escherichia coli HB101(Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Lab. Press,New York, 1989) was transformed with the ligation product to constructplasmid pChi641LGM40.

The plasmid pChi641LGM40 constructed above was cleaved with restrictionenzyme ClaI (Takara Shuzo Co., Ltd.) and blunted using DNA Blunting Kit(Takara Shuzo Co., Ltd.), followed by cleavage with MluI (Takara ShuzoCo., Ltd.) to obtain a fragment of ca. 5.68 kb comprising the L-chaincDNA. Separately, the expression vector pChi641HGM4 for H-chain ofanti-GD3 chimeric antibody [J. Immunol. Methods, 167, 271 (1994)] wascleaved with restriction enzyme XhoI (Takara Shuzo Co., Ltd.) andblunted using DNA Blunting Kit (Takara Shuzo Co., Ltd.), followed bycleavage with MluI (Takara Shuzo Co., Ltd.) to obtain a fragment of ca.8.40 kb comprising the H-chain cDNA. The thus obtained fragments wereligated using DNA Ligation Kit (Takara Shuzo Co., Ltd.) and Escherichiacoli HB101 (Molecular Cloning: A Laboratory Manual, Cold Spring HarborLab. Press, New York, 1989) was transformed with the ligation product toconstruct tandem expression vector pChi641LHGM4 for anti-GD3 chimericantibody.

2. Preparation of a Producing Cell Using Rat Myeloma Cell YB2/0

The tandem expression vector pChi641LHGM4 for anti-GD3 chimeric antibodyconstructed in Example 1-1 (5 μg) was introduced into YB2/0 rat myelomacells (4×10⁶ cells/ml) by electroporation [Cytotechnology, 3, 133(1990)], and the resulting cells were suspended in 40 ml ofRPMI1640-FBS(10) [RPMI1640 medium containing 10% FBS (GIBCO BRL)] andput into wells of a 96-well culture plate (Sumitomo Bakelite Co., Ltd.)in an amount of 200 μl/well. After culturing in a 5% CO₂ incubator at37° C. for 24 hours, G418 was added to give a concentration of 0.5mg/ml, followed by further culturing for 1 to 2 weeks. The culturesupernatants were collected from the wells in which a colony oftransformant exhibiting G418-resistance appeared and growth wasobserved, and the antigen-binding activity of anti-GD3 chimericantibodies in the supernatants was measured by ELISA as described inExample 1-3.

The transformants in the wells containing culture supernatants in whichthe production of anti-GD3 chimeric antibody was observed were treatedin the following manner in order to increase the antibody production byutilizing the DHFR gene amplification system. That is, the transformantcells were suspended in RPM11640-FBS(10) containing 0.5 mg/ml G418 and50 nM methotrexate (a DHFR inhibitor; hereinafter referred to as MTX;Sigma Chemical Co.) at a density of 1 to 2×10⁵ cells/ml and put intowells of a 24-well plate (Greiner) in an amount of 2 ml per well.Culturing was carried out in a 5% CO₂ incubator at 37° C. for 1 to 2weeks to obtain transformants exhibiting the resistance to 50 nM MTX.

The antigen-binding activity of anti-GD3 chimeric antibodies in theculture supernatants in the wells in which the growth of transformantwas observed was measured by ELISA as described in Example 1-3. Thetransformants in the wells containing culture supernatants in which theproduction of anti-GD3 chimeric antibody was observed were treated in amanner similar to the above with the MTX concentration successivelyraised (100 nM and 200 nM) to finally obtain transformants which arecapable of growing in RPMI1640-FBS(10) containing 0.5 mg/ml G418 and 200mM MTX and which highly produce anti-GD3 chimeric antibodies. Theobtained transformants were cloned by carrying out limiting dilutiontwice.

The thus obtained anti-GD3 chimeric antibody-producing transformantclone 7-9-51 was deposited with the National Institute of Bioscience andHuman-Technology, Agency of Industrial Science and Technology, 1-3,Higashi 1-chome, Tsukuba-shi, Ibaraki, Japan, on Apr. 5, 1999 as FERMBP-6691.

3. Measurement of GD3-Binding Activity of Antibodies (ELISA)

The GD3-binding activity of antibodies was measured in the followingmanner.

GD3 (4 nmol) was dissolved in 2 ml of ethanol containing 10 μg ofdipalmitoyl phosphatidylcholine (Sigma Chemical Co.) and 5 μg ofcholesterol (Sigma Chimical Co.), and 20 μl portions of the solution (40pmol/well) were put into wells of a 96-well plate for ELISA (Greiner).After air-drying, PBS containing 1% bovine serum albumin (Sigma ChemicalCo.; hereinafter referred to as BSA) (this PBS is hereinafter referredto as 1% BSA-PBS) was added to the wells in an amount of 100 μl/well,followed by reaction at room temperature for one hour to block theremaining active groups. Then, the 1% BSA-PBS was discarded, and 50 μleach of the culture supernatant of transformant or variously dilutedsolutions of a purified human chimeric antibody was respectively addedto the wells, followed by reaction at room temperature for one hour.After the reaction, the wells were washed with PBS containing 0.05%Tween 20 (Wako Pure Chemical Industries, Ltd.) (hereinafter referred toas Tween-PBS). To each well was added 50 μl of peroxidase-labeled goatanti-human IgG (H & L) antibody solution (American Qualex) diluted3000-fold with 1% BSA-PBS as a secondary antibody solution, followed byreaction at room temperature for one hour. After the reaction, the wellswere washed with Tween-PBS, and 50 μl of ABTS substrate solution [asolution prepared by dissolving 0.55 g of2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) ammonium in 1 lof 0.1 M citrate buffer (pH 4.2) and adding thereto, just before use, 1μl/ml hydrogen peroxide] was added to each well to develop color. Then,the absorbance at 415 nm (hereinafter referred to as OD 415) wasmeasured.

Example 2

The anti-GD3 antibody-producing transformant clone 7-9-51 (FERM BP-6691)was adapted to a serum-free medium in the following manner. In allsteps, culturing was carried out by static subculture in a T flask underthe following conditions: temperature, 37° C.; CO₂ concentration, 5%;amount of culture, 5 ml. When the cells were passaged, the whole cultureliquor was replaced with a fresh medium by centrifugation.

FERM BP-6691 was inoculated into a serum-containing medium prepared byadding bovine serum albumin (BSA; JRH), insulin (Life Technologies,Inc.) and transferrin (Life Technologies, Inc.) to a basal medium foradaptation to serum-free conditions comprising IMD medium (LifeTechnologies, Inc.) and 200 nM MTX (Sigma Chemical Co.) at a celldensity of 2 to 4×10⁵ cells/ml, and subcultured (period for one passage:2 to 4 days).

The cells obtained by the above subculturing were subcultured in aserum-containing medium prepared by adding 5% (v/v) γ-ray-irradiateddialyzed fetal bovine serum (dFBS; Life Technologies, Inc.) and 100 nMT3 to the above basal medium. Then, subculturing of the cells wasserially carried out using the following media: a medium prepared byadding 0.2% (w/v) BSA, 50 mg/l insulin and 50 mg/l transferrin to theabove basal medium (9 passages, 27 days); a medium prepared by adding0.2% (w/v) BSA, 20 mg/l insulin and 20 mg/l transferrin to the abovebasal medium (one passage, 3 days); a medium prepared by adding 0.1%(w/v) BSA, 20 mg/l insulin and 20 mg/l transferrin to the above basalmedium (one passage, 3 days); and a medium prepared by adding 0.05%(w/v) BSA, 10 mg/l insulin and 10 mg/l transferrin to the above basalmedium (one passage, 3 days).

In preparing a cell line adapted to a serum-free medium, the viabilityof cells lowered intermittently during the culturing for 27 days in themedium prepared by adding 0.2% (w/v) BSA, 50 mg/l insulin and 50 mg/ltransferrin to the above basal medium. As a result of attempts to solvethis problem, the cells could be adapted to a serum-free medium withoutlowering of the viability of cells by inoculating the cells into themedium at a density of 4×10⁵ cells/ml.

Cloning of the rat cells adapted to a serum-free medium was carried outby limiting dilution in the following manner.

A cell suspension was prepared and put into wells of 96-well plates inan amount of 0.25cell/well and 0.2 ml/well. The cells were seeded in1632 wells in total, and as a result, 72 clones were obtained. Theprocedure was repeated on a larger scale using 6-well plates and thenErlenmeyer flasks, and 3 clones were selected based on the productivityand growth. Among these, one having a high productivity was designated61-33 γcell line. The cell line 61-33γadapted to a serum-free medium wasdeposited with the National Institute of Bioscience andHuman-Technology, Agency of Industrial Science and Technology, 1-3,Higashi 1-chome, Tsukuba-shi, Ibaraki, Japan, on Oct. 13, 2000 as FERMBP-7325, according to the Treaty of Budapest.

The thus obtained cell line 61-33γ adapted to a serum-free medium couldbe stably subcultured for a period of 110 days by carrying outsubculturing in a medium prepared by adding 0.2% (w/v) BSA, 10 mg/linsulin, 10 mg/l transferrin and 200 nM MTX to the above serum-freebasal medium (period for one passage: 3 to 5 days).

FERM BP-7325 was inoculated into a serum-free medium prepared by adding0.1% (w/v) BSA and 200 nM MTX to Hybridoma-SFM at a density of 3×10⁶cells/ml, and subjected to batch culture in a 5% CO₂ incubator at 37° C.for 3 days. At the completion of culturing, the cell density was17.5×10⁶ cells/ml and the antibody concentration in the supernatant was39 mg/l.

On the other hand, FERM BP-6691 was inoculated into a serum-containingmedium prepared by adding 10% (v/v) dFBS and 200 nM MTX to IMD medium ata density of 3×10⁶ cells/ml, and subjected to batch culture in a 5% CO₂incubator at 37° C. for 3 days. At the completion of culturing, the celldensity was 14.2×10⁶ cells/ml and the antibody concentration in thesupernatant was 28 mg/l.

Example 3

Batch culture of FERM BP-7325 was carried out using a spinner flaskcontaining a serum-free medium.

FERM BP-7325 was subjected to static culture using a T-225-cm² flaskcontaining 30 ml of a serum-free medium (Hybridoma-SFM; LifeTechnologies, Inc.) in a 5% CO₂ incubator at 37° C. for 3 days. Theresulting FERM BP-7325 was inoculated into 0.7 l of a serum-free medium(Hybridoma-SFM; Life Technologies, Inc.) in a 1-1 spinner flask (ShibataHario Co., Ltd.) at a density of 3×10⁵ cells/ml.

Culturing was carried out with stirring at 30 rpm while the pH ofculture was controlled at 7.1±0.1 and the dissolved oxygen concentrationwas controlled at 5±0.2 ppm. Aeration was carried out by supplying amixed gas of air, oxygen and carbon dioxide through a porous Teflon tubeinstalled in the spinner flask. The pH was controlled by changing theratio between air and carbon dioxide, and by supplying 1 M sodiumcarbonate solution. The dissolved oxygen concentration was controlled bychanging the ratio between air and oxygen.

The results are shown in FIG. 1 and FIG. 2.

As shown in FIG. 1 and FIG. 2, the cells showed logarithmic growth untilthe 3rd day of culturing, but thereafter the specific growth ratelowered. The viable cell density reached a maximum of ca. 3×10⁶ cells/mlon the 4th day, and then rapidly lowered. On the 6th day of culturing,the viability lowered to less than 10%, and the culturing was finished.

The antibody production by culturing for 6 days was 45 mg/l and thus theantibody production rate by batch culture was 7.5 mg/l/day.

Example 4

Fed-batch culture of FERM BP-7325 was carried out using a spinner flaskcontaining a serum-free medium.

FERM BP-7325 was subjected to static culture using a T-225-cm² flaskcontaining 30 ml of a serum-free medium (Hybridoma-SFM; LifeTechnologies, Inc.) in a 5 CO₂ incubator at 37° C. for 3 days. Theresulting FERM BP-7325 was inoculated into 0.7 l of Hybridoma-SFM in a1-1 spinner flask (Shibata Hario Co., Ltd.) at a density of 3×10⁵cells/ml.

For the purpose of compensating the consumption of amino acids estimatedfrom the specific consumption rate thereof, a feed medium comprisingamino acids (0.140 g/l L-alanine, 0.470 g/l L-argininemonohydrochloride, 0.159 g/l L-asparagine monohydrate, 0.168 g/lL-aspartic acid, 0.511 g/l L-cystine dihydrochloride, 0.420 g/lL-glutamic acid, 4.677 g/l L-glutamine, 0.168 g/l glycine, 0.235 g/lL-histidine monohydrochloride dihydrate, 0.588 g/l L-isoleucine, 0.588g/l L-leucine, 0.818 g/l L-lysine monohydrochloride, 0.168 g/lL-methionine, 0.370 g/l L-phenylalanine, 0.224 g/l L-proline, 0.235 g/lL-serine, 0.532 g/l L-threonine, 0.090 g/l L-tryptophan, 0.581 g/lL-tyrosine disodium dihydrate, and 0.526 g/l L-valine), vitamins (0.0728mg/l d-biotin, 0.0224 g/l calcium D-pantothenate, 0.0224 g/l cholinechloride, 0.0224 g/l folic acid, 0.0403 g/1 myo-inositol, 0.0224 g/lniacinamide, 0.0224 g/l pyridoxal hydrochloride, 0.00224 g/l riboflavin,0.0224 g/l thiamine hydrochloride, and 0.0728 mg/l cyanocobalamin), 0.2g/l insulin, 0.2 g/l transferrin, and 1.6 g/l albumin, which wereadjusted to higher concentrations than usual concentrations foraddition, was added in 0.07-1 portions once a day or with less frequencywhen the cumulative viable cell density exceeded 4×10⁶ cells/ml×day. Inother words, 0.07 l of the feed medium was added on the 3rd, 5th, 6th,7th and 8th days of culturing. On the 3rd day of culturing andthereafter, 100 g/l glucose solution was added at appropriate times sothat the glucose concentration in the culture immediately after additionwould be ca. 2500 mg/l.

Culturing was carried out with stirring at 30 rpm while the pH ofculture was controlled at 7.1±0.1 and the dissolved oxygen concentrationwas controlled at 5±0.2 ppm. Aeration was carried out by supplying amixed gas of air, oxygen and carbon dioxide through a porous Teflon tubeinstalled in the spinner flask. The pH was controlled by changing theratio between air and carbon dioxide, and by supplying 1 M sodiumcarbonate solution. The dissolved oxygen concentration was controlled bychanging the ratio between air and oxygen.

The results are shown in FIG. 1 and FIG. 2.

The cells showed logarithmic growth until the 5th day of culturing.Though the specific growth rate lowered on and after the 5th day ofculturing, the viable cell density reached ca. 1×10⁷ cells/ml on the 6thday of culturing.

After the viable cell density reached a maximum, the viable cell densityand viability lowered slowly. On the 10th day of culturing, theviability lowered to less than 20%, and the culturing was finished.

The antibody production by culturing for 10 days was 260 mg/l and thusthe antibody production rate by fed-batch culture was 26.0 mg/l/day,which means that the antibody production rate improved as compared withthat by batch culture on the same scale, i.e. about 3.5 times that bybatch culture.

Example 5

Continuous culture of FERM BP-7325 was carried out using a spinner flaskcontaining a serum-free medium. In order to carry out perfusion in thecontinuous culture, solid-liquid separation of concentrated culturecontaining the cells and culture supernatant was conducted by using acentrifuge.

FERM BP-7325 was subjected to static culture using a T-225-cm² flaskcontaining 30 ml of a serum-free medium (Hybridoma-SFM; LifeTechnologies, Inc.) in a 5% CO₂ incubator at 37° C. for 3 days. Theresulting FERM BP-7325 was inoculated into 1 l of a medium prepared byadding 18% (v/v) supplementation medium comprising amino acids (0.220g/l L-alanine, 0.739 g/l L-arginine monohydrochloride, 0.264 g/lL-asparagine monohydrate, 0.220 g/l L-aspartic acid, 0.803 g/l L-cystinedihydrochloride, 0.660 g/l L-glutamic acid, 7.34 g/l L-glutamine, 0.264g/l glycine, 0.370 g/l L-histidine monohydrochloride dihydrate, 0.924g/l L-isoleucine, 0.924 g/l L-leucine, 1.285 g/l L-lysinemonohydrochloride, 0.264 g/l L-methionine, 0.581 g/l L-phenylalanine,0.352 g/l L-proline, 0.370 g/l L-serine, 0.836 g/l L-threonine, 0.141g/l L-tryptophan, 0.915 g/l L-tyrosine disodium dihydrate, and 0.827 g/lL-valine), vitamins (0.114 mg/l d-biotin, 0.0352 g/l calciumD-pantothenate, 0.0352 g/l choline chloride, 0.0352 g/l folic acid,0.0634 g/1 myo-inositol, 0.0352 g/l niacinamide, 0.0352 g/l pyridoxalhydrochloride, 0.00352 g/l riboflavin, 0.0352 g/l thiaminehydrochloride, and 0.114 mg/l cyanocobalamin), 0.3 g/l insulin, 0.3 g/ltransferrin, and 2.5 g/l albumin to Hybridoma-SFM in a 1-1 spinner flask(Shibata Hario Co., Ltd.) at a density of 3×10⁵ cells/ml.

Perfusion was started when the cell density reached 1×10⁶ cells/ml.Then, the perfusion rate, i.e. the rate of medium replacement per daywas raised according to the cell count, and when it was made 1 l/day,the viable cell density entered the maintenance phase. As an apparatusfor solid-liquid separation, a small-sized continuous centrifuge forcell culture (Lab-II; Sobal) was used.

Culturing was carried out for 35 days, during which the small-sizedcontinuous centrifuge for cell culture was operated at 800 rpm from thestart of culturing till the viable cell density reached 1×10⁷ cells/ml,and at 400 rpm (18×G) after the viable cell density reached 1×10⁷cells/ml.

When the rotation rate of the centrifuge was set at 800 rpm, almost allthe cells were recovered within the system and only the culturesupernatant containing few cells was discharged from the system. Whenthe rotation rate of the centrifuge was set at 400 rpm, ½ of all thecells were discharged from the system, and thus the number of cellsdischarged from the system was counterbalanced by the number of cellsincreased by growth to keep the cell density constant.

The viable cell density and viability of FERM BP-7325 during theperfusion culture are shown in FIG. 3.

As shown in FIG. 3, the viable cell density was maintained at 1×10⁷cells/ml for 30 days after the 5th day of culturing and the viabilitywas maintained at 90% through the culturing period. The antibodyproduction by culturing for 35 days was 2200 mg/l and thus the antibodyproduction rate by perfusion culture was 62.9 mg/l/day.

Example 6

FERM BP-7325 was inoculated into a medium prepared by adding 20 mg/linsulin to Hybridoma-SFM (Life Technologies, Inc.) containing no insulinin a T-75 flask, and subcultured. After the completion of culturing, theculture was centrifuged to remove the supernatant and to recover thecells. The recovered cells were inoculated into Hybridoma-SFM containingno insulin in a T-75 static culture flask, and cultured for 3 days.After the completion of culturing, the culture was centrifuged to removethe supernatant and to recover the cells.

The recovered cells were suspended in media prepared by respectivelyadding 0, 5, 10 and 20 mg/l insulin to Hybridoma-SFM containing noinsulin and inoculated into T-flasks, followed by static culture in a 5%CO₂ incubator at 37° C. for 6 days.

After the completion of culturing, the viable cell count and antibodyconcentration in each culture were measured, and the specific productionrate of antibody was calculated.

The results are shown in Table 1.

TABLE 1 Insulin concentration Specific production rate (mg/l)(μg/10⁶/day) 0 13.1 5.0 9.0 10.0 7.6 20.0 7.8

As shown in Table 1, the highest productivity of antibody was obtainedby use of the medium which was not supplemented with insulin, i.e. themedium containing insulin remaining in a trace amount, and theproductivity was high also in the medium containing 5 mg/l insulin.

The cell growth rate lowered a little in an insulinconcentration-dependent manner but a remarkable lowering was notobserved.

INDUSTRIAL APPLICABILITY

The present invention provides a process for producing desiredpolypeptides using rat cells. Specifically, the antibodies obtained bythe process of the present invention have high ADCC activity and areuseful as pharmaceutical agents.

The invention claimed is:
 1. A process for producing a polypeptide,comprising: (a) selecting a rat cell line that has been adapted to growin a serum-free medium, wherein the rat cell line is adapted to grow ina serum-free medium by performing the step of inoculating rat cells intoa medium at a cell density of 1×10⁵ to 1×10⁶ cells/ml, said mediumcontaining added physiologically active substances consisting of bovineserum albumin, insulin and transferrin, and culturing said cells in saidmedium, and subculturing the cultured cells by repeating said step underconditions of stepwise decreasing the added amounts of bovine serumalbumin, insulin and transferrin to 0.05 (w/v) %, 10 mg/1 and 10 mg/1,respectively, wherein the resulting rat cells can be subcultured in aserum-free medium for two months or more; (b) inoculating a serum-freemedium with the selected rat cell line, and culturing said selected ratcell line to permit expression of a desired polypeptide; and (c)recovering the desired polypeptide from the culture.
 2. The processaccording to claim 1, wherein the rat cell is a myeloma cell or a hybridcell derived from a myeloma cell.
 3. The process according to claim 1,wherein the rat cell is YB2/3 HL.P2.G11.16 Ag.20 (ATCC CRL 1662).
 4. Theprocess according to claim 1, wherein the cell is a cell to which arecombinant DNA comprising DNA encoding the desired polypeptide isintroduced.
 5. The process according to claim 1, wherein the culturingis carried out by batch culture, fed-batch culture or perfusion culture.6. The process according to claim 1, comprising adding a nutrient factorto the medium during the culturing, wherein the nutrient factor is atleast one member selected from the group consisting of glucose, an aminoacid and a vitamin.
 7. The process according to claim 1, wherein thedesired polypeptide is an immunologically functional molecule.
 8. Theprocess according to claim 7, wherein the immunologically functionalmolecule is a protein or a peptide.
 9. The process according to claim 8,wherein the protein or peptide is an antibody, an antibody fragment or afusion protein comprising an antibody Fc region.
 10. The processaccording to claim 9, wherein the antibody is an antibody recognizing atumor-related antigen, an antibody recognizing an allergy- orinflammation-related antigen, an antibody recognizing a circulatorydisease-related antigen, an antibody recognizing an autoimmunedisease-related antigen, or an antibody recognizing a viral or bacterialinfection-related antigen.
 11. The process according to claim 1, whereinthe antibody recognizing a tumor-related antigen is an anti-GD2antibody, an anti-GD3 antibody, an anti-GM2 antibody, an anti-HER2antibody, an anti-CD52 antibody, an anti-MAGE antibody, an anti-basicfibroblast growth factor antibody, an anti-basic fibroblast growthfactor receptor antibody, an anti-FGF8antibody, an anti-FGF8 receptorantibody, an anti-insulin-like growth factor antibody, an anti-PMSAantibody, an anti-vascular endothelial cell growth factor antibody, oran anti-vascular endothelial cell growth factor receptor antibody; theantibody recognizing an allergy- or inflammation-related antigen is ananti-interleukin 6 antibody, an anti-interleukin 6 receptor antibody, ananti-interleukin 5 antibody, an anti-interleukin 5 receptor antibody, ananti-interleukin 4 antibody, an anti-interleukin 4 receptor antibody, ananti-tumor necrosis factor antibody, an anti-tumor necrosis factorreceptor antibody, an anti-CCR4 antibody, an anti-chemokine antibody, oran anti-chemokine receptor antibody; the antibody recognizing acirculatory disease related antigen is an anti-GpIIb/IIIa antibody, ananti-platelet-derived growth factor antibody, an anti-platelet-derivedgrowth factor receptor antibody, or an anti-blood coagulation factorantibody; the antibody recognizing an autoimmune disease-related antigenis an anti-auto-DNA antibody; and the antibody recognizing a viral orbacterial infection-related antigen is an anti-gp120 antibody, ananti-CD4 antibody, an anti-CCR4 antibody, or an anti-verotoxin antibody.12. The process according to claim 10, wherein the antibody is ananti-GD3 human chimeric antibody, a humanized anti-interleukin 5receptor cc chain antibody, or an anti-GM2 human CDR-grafted antibody.13. A rat myeloma cell line, or hybrid cell line derived from a ratmyeloma cell, adapted to a serum-free medium, wherein said adapted cellline is obtained by performing the step of inoculating rat myelomacells, or hybrid cells derived from rat myeloma cells, into a medium ata cell density of 1×10⁵ to 1×10⁶ cells/ml, said medium containing addedphysiologically active substances consisting of bovine serum albumin,insulin and transferrin, and culturing said cells in said medium, andsubculturing the cultured cells by repeating said step under conditionsof stepwise decreasing the added amounts of bovine serum albumin,insulin and transferrin to 0.05 (w/v) %, 10 mg/1 and 10 mg/1,respectively, wherein the adapted cell line can be subcultured in aserum-free medium for two months or more.
 14. The rat myeloma cell line,or hybrid cell line of claim 13, wherein said rat myeloma cell isselected from the group consisting of Y3AG1.2.3. (ATCC CRL 1631), Y0(ECACC No:85110501) and YB2/0 (ATCC CRL 1662).
 15. A rat cell lineadapted to a serum-free medium, which is 61-33γ(FERM BP-7325).